Using a PC Power Supply for Accessories
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JohnBoy
Joined: May 14, 2008
Topics: 110 Replies: 517
Topics: 110
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When I first started building out my layout, I wired all my accessories to the 14-volt fixed-volt jack on the back of my MTH Z4000 transformer. For several years, this served me quite well, and never seemed to interfere with the running of trains.
Over the years, I started adding lots of new buildings and accessories, most of which light up in some way or another. Over time, this very gradually started causing a voltage drop on the 14-volt line. That's most likely because I had too many lights drawing from that little fixed-volt tap on the Z4K transformer.
When I embarked on my Union Station project, and started lighting up various sections of it, I bought a second little transformer just to power it. This worked well for a while, but eventually I added so many little lights to the station, that I found that I could not light up the whole station at the same time, as the little transformer would start flickering and dimming under the load.
It was time to start fresh and think about how I wanted to power my lighted buildings. Transformers - particularly hobby transformers that are designed to operate model RR trains - are some of the most expensive options when measured on a watt-per-dollar basis. My MTH Z4000 is a 400-watt transformer, and cost nearly $400. I wanted to get something that was powerful enough to let me expand my lighted buildings and accessories for years to come, but didn't cost so much.
I read a couple of threads on the OGR Forum, and those threads also had links to other articles which stepped through the process of converting a PC Power Supply Unit (PSU) to be used as a general-purpose fixed-volt transformer. This is a nice option because PC PSUs are very inexpensive - I suspect due mostly to the fact that they are produced in such large quantities.
Perusing Newegg.com showed me that there were dozens of high-quality options for PC PSUs available, ranging from 200-watt to 1500-watt units. And they are all very reasonably priced. I found a 550-watt PSU for $35 shipped, and went with it.
The conversion was pretty straight-forward, if you're reasonably comfortable with a soldering iron and some basic electrical knowledge. You essentially combine all wires of the same color together, creating high-capacity taps for 3.3-volt, 5-volt, and 12-volt lines. You need to place some kind of small load on the 5-volt line, just to trick the PSU into believing there is a motherboard running on it, and there are a couple other wiring steps that need to be done. Here is the tutorial I followed:
Converting a PC Power Supply
I chose to solder each output wire individually to a larger "bus" wire. So I gathered all the black wires (which are the returns, or negatives for all the colored wires) and soldered each of them to a 14-gauge stranded wire. Similarly, I soldered all the red wires (+5 volts DC) to another 14-gauge wire, all the orange wires (+3.3 volts DC) to another 14-gauge wire, and all the yellow wires (+12 volts DC) to another 14-gauge wire. I used wooden strips to create "channels" for each of these 4 bus wires to rest in, taking care to staple them down into place before gluing the sticks in between them. This is to protect them from touching each other and shorting out. I then simply connected each of these 14-gauge bus wires to a terminal block, and then ran bus wires from the terminal block to various points on my layout.
Why 12-volts DC Is Better
I want to touch upon why it is I am convinced that 12-volts DC is the best approach for powering your layout accessories. For one thing, the power that these PC PSUs provide is true, filtered and regulated Direct Current (DC).
The "regulated" term here means that the PSU will put out the full voltage no matter how many devices you hook up to it - up until the capacity is exceeded (or a little bit before it). So you don't have to worry about voltage-drop until you've hooked up a lot of accessories - in my case, nearly 550 watts worth.
The term "filtered" here means that it's not just rectified AC - which will suffice for a lot of things that require DC, but not all of them. Some devices must have a pure, solid and even pressure of voltage in order to operate properly. Many of the animated billboard signs, strobe lights, arc-welding lights, and other popular devices from Miller Engineering, Miniatronics, and other vendors require true DC. It is becoming increasingly popular to use LEDs instead of mini incandescent bulbs for many lighting projects on train layouts. And LEDs require DC. I use several 555 timer chips on my layout to create blinking platform lights behind my train station, and flashing strobes on top of my suspension bridge. And the 555 timer chips - like most ICs - require true DC.
Since incandescent bulbs will also work on DC, it makes sense to just use DC for all your accessories. Even though your incandescent bulbs may have a slightly reduced service life on DC*, it seems to me a small price to pay for the convenience of having DC power available to all devices that may require it.
Another consideration is that 12-volts DC is a very popular operating voltage. I would hazard a guess that there are more components designed to run on 12-volts than any other voltage. Fans, incandescent bulbs, timers, relays, and even some of the newer multi-chip LEDs all run on 12 volts DC. The newest models of Cold-Cathode Florescent tubes (CCFLs) also run on 12-volts DC. 12 volts DC is also a very convenient voltage for wiring up modern white and blue LEDs, most of which operate on 3 to 3.5 volts, and so if you wire them in series of 4 LEDs, you can feed them 12 volts DC and they will work fine, without the need for a bridge rectifier and capacitor.
It turns out that 12 VDC is one of the most ubiquitous power requirements out there, and it has opened up a whole world of components to me that I can now run directly - without having to wire in bridge rectifiers, capacitors, and resistors to convert the 14 VAC to 12 VDC.
Epilogue
It works like a charm. What I had to do next is go back and retro-fit some of my larger buildings with 12-volt lighting, because I had originally installed 14- to 16-volt bulbs in them, and these were just too dim on 12 volts. Looking in the outdoor lighting section at Home Depot, I found some 12-volt halogen bulbs in 4-packs for only $5. They stock a variety of these: 4, 5, 7, 10, 15, and 20 watt types. I found that the 4-watt versions were perfect - very bright, but still don't burn too hot to trust inside a model building.
If you're looking for an inexpensive, convenient, reliable power supply for your model railroad accessories, start shopping for a PC PSU. Check Newegg, Tiger Direct, or PriceWatch for terrific bargains on a wide range of capacities.
* There is some controversy that incandescent bulbs will not last quite as long on DC as on AC, but the alleged difference in lifespan is not significant. And since most of the mini-incandescent bulbs I have encountered in the model RR hobby have an average expected service life of 10,000 to 20,000 hours, they are likely to last 30 years or more anyway. So a slight reduction in service life is not going to be noticeable, unless of course you run your layout lights 24/7/365.
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auaero97
Joined: Jun 22, 2010
Topics: 0 Replies: 2
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John,
Would you consider posting a schematic on how you wired this to work? The picture tells part of the story. My biggest question I suppose is how to trick the power supply into thinking there is a load. I do have an ATX power supply tester which tricks it into thinking there is a load. I had to purchase one once to determine that a new power supply I had purchased was actually dead. I suppose I could use that, but then I would be without my tester. I did read somewhere on the net about shorting two of the pins with a paperclip, but without specifics I would be concerned about ruining it. I have thought about trying this for sometime, I'm glad that someone had tried it. I have found your site very informative.
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JohnBoy
Joined: May 14, 2008
Topics: 110 Replies: 517
Topics: 110
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auaero97 - I will try to do that some day, but I am currently under water so I don't know when I'll be able to get to it.
For your big question: how to trick the PSU into thinking there is a load - all you need to do is place a small load on the 5-volt line. This can be an incandescent light bulb, according to some things I've read. I didn't do the light bulb, because what happens when it burns out? I guess your PSU would stop working until you replaced it?
I used a resistor - a 10-Ohm, 10+ watt resistor. I used simple wire as twisty-ties to secure the body of the resistor to the metal grating outside the fan, as the resistor can get rather warm during operation, and the fan blows the hot air off of the resistor and away from the PSU.
I strongly recommend that you read the article that I used (mentioned above). It is very thorough.
Post back if you have any questions, Ok?
John
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auaero97
Joined: Jun 22, 2010
Topics: 0 Replies: 2
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John,
Thanks for the link to the article. I believe it will help. The fact that they have a video there is pretty cool also. I guess I didn't see the link before for the article you mentioned. I tried doing a search, but couldn't come up with anything useful. I had a friend throwing an old computer out so I asked if I could take the power supply. It's rather small (250W), but if I were to screw it up, I'm not out the money for a good power supply.
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JohnBoy
Joined: May 14, 2008
Topics: 110 Replies: 517
Topics: 110
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Just read that article carefully. One of the things they caution about is making sure you wait at least a couple days after unplugging before opening the PSU. There are banks of capacitors in there that pack quite a charge, and it could give you a real jolt. But they will drain out after two days, and then it's safe.
Post back with your results - I'm interested in learning from your experiences.
Cheers,
John
Thank you for this article.I hope to have my layout underway shortly.This power conversion looks as though it would be versitile as well as economical.
Progress: